Loop through marking

#dataTable is a DataTable script parameter. 
markedRows = Document.ActiveMarkingSelectionReference.GetSelection(dataTable)

print "Selected rows:\t" + str(markedRows.IncludedRowCount) #same as str(markedRows.AsIndexSet().Count
print "Total rows:\t"    + str(markedRows.TotalRowCount)
print "Hidden rows:\t"   + str(markedRows.ExcludedRowCount)

#Loop through marked rows. "symbol" is a column name
for r in markedRows.AsIndexSet(): 
   print "row # " + str(r) + " value:\t" + dataTable.Columns["symbol"].RowValues.GetFormattedValue(r)


If you want to use a specific marking from a specific (Treemap) visualization, then:

#get a reference to the vis, datatable and marking. vis is a script parameter 
myTreemap = vis.As[Treemap]()
myTreemapDataTable = myTreemap.Data.DataTableReference
myTreemapMarking = myTreemap.Data.MarkingReference

for markedRow in myTreemapMarking.GetSelection(myTreemapDataTable).AsIndexSet():
   myTreemapDataTable.Columns["symbol"].RowValues.GetFormattedValue(markedRow)